Remove a few more 'mutable' words

Didn't see these before because they live in non-Linux code.

Author: marijnh

src/lib/macos_OS.rs

@@ -63,7 +63,7 @@ fn dylib_filename(str base) -> str {
 
 fn pipe() -> tup(int, int) {
     let vec[mutable int] fds = vec(mutable 0, 0);
-    assert (OS.libc.pipe(Vec.buf[mutable int](fds)) == 0);
+    assert (OS.libc.pipe(Vec.buf(fds)) == 0);
     ret tup(fds.(0), fds.(1));
 }
 
@@ -73,7 +73,7 @@ fn fd_FILE(int fd) -> libc.FILE {
 
 fn waitpid(int pid) -> int {
     let vec[mutable int] status = vec(mutable 0);
-    assert (OS.libc.waitpid(pid, Vec.buf[mutable int](status), 0) != -1);
+    assert (OS.libc.waitpid(pid, Vec.buf(status), 0) != -1);
     ret status.(0);
 }
 

src/lib/win32_OS.rs

@@ -53,7 +53,7 @@ fn dylib_filename(str base) -> str {
 
 fn pipe() -> tup(int, int) {
     let vec[mutable int] fds = vec(mutable 0, 0);
-    assert (OS.libc._pipe(Vec.buf[mutable int](fds), 1024u,
+    assert (OS.libc._pipe(Vec.buf(fds), 1024u,
                         libc_constants.O_BINARY()) == 0);
     ret tup(fds.(0), fds.(1));
 }